Dissertations / Theses on the topic 'Pressure Swing Adsorption'

Thesis (Masters Diploma (Mechanical engineering)--Cape Technikon, Cape Town, 1993
The main objective of the work outlined in tills project is to create an awareness of Pressure Swing Adsorption (PSA) Processes, their application to oxygen production systems in the RSA and the construction and testing of a pilot plant, built to assess an overseas design. Available oxygen PSA technology was examined from a theoretical approach, right through to practical applications. The aim was not to re-invent the technology, but to review what technology is available and to assess its suitability for the South African Industrial Sectors. This was undertaken by investigating all PSA processes that are available to market the product to industry. The technology review includes an investigation of overseas PSA technologies and compares these modes of technology with the technology that is readily available to Afrox Limited, a major gas supplier in South Africa. This resulted in the technology from the British Oxygen Company being thoroughly reviewed, examined and compared to various other modes of technology. The basic principals of adsorption are discussed to give the reader an understanding of the factors that influence efficient adsorption and adsorbent regeneration. The parameters that defme when adsorption separation processes are applicable to the separation of atmospheric gases are also discussed. The different types of PSA plant layout are discussed in great detail and it is explained when each plant layout type would be used.

In this dissertation, an algorithm for modelling cyclic processes is designed. In principle, the algorithm could be used for any cyclic processes. Air separation using rapid pressure swing adsorption (RPSA) is used as an illustration of the algorithm. The first step in the algorithm is to identify physical phenomena to be included in or omitted from a model. The effect of the external fluid film resistance at the surface of an adsorbent particle is studied in detail using a linear driving force model. A simple method that could be used to determine quickly the importance of film resistance in cyclic processes is developed. For the RPSA cases considered, it transpires that the film resistance could be neglected. The use of concentrations as dependent variables and of Danckwerts boundary conditions (BCs) in an axially dispersed plug flow (ADPF) model for the modelling of RPSA are shown to violate the conservation of mass. To conserve mass in an ADPF model, we recommend adopting mole fractions as dependent variables and using modified BCs. The modified BCs advocated preserve the original argument of Danckwerts and are also physically sound. The RPSA models are then solved numerically using the method of orthogonal collocation. An improved method that calculates accurately quantities involving time integrals, and also minimises the number of decision parameters that need to be made by the users of the computer programs, is introduced. A major achievement of this work is the development of two novel algorithm features for the transient simulation of cyclic processes that exhibit cyclic steady state (CSS). The first feature of the algorithm is an a priori rational stopping criterion to determine the CSS unambiguously. The stopping criterion ensures that neither is the progress towards CSS truncated prematurely nor is computer time wasted by simulating an unnecessarily large number of cycles. The second feature of the algorithm is a reduction of the number of cycles required to reach the CSS while ensuring that the CSS is certainly determined.

Pressure swing adsorption is a method for separating gases by selective adsorption. It is being used increasingly in industry where for some applications, including air separation, the number of plants have increased at a near exponential rate in recent years. However, despite the many hundred different plant configurations and cycles, there is still a lack of understanding of the basic process steps and plenty of scope for achieving even better plant performances. This study examines experimentally and theoretically a two bed process for separating oxygen from air using a zeolite adsorbent. A plant was designed and built to incorporate the novel feature of recycling waste gas from the purge and depressurization steps back into the feed line and also to investigate conventional purge, backfill and combined cycles. Theoretical modelling had predicted that large amounts of waste gas could be recycled without loss in product oxygen concentration, but causing an improvement in oxygen yield. This was verified experimentally, demontrating potential energy savings. For each cycle investigated the product oxygen concentration and yield were optimized over a range of product amounts per cycle while continually monitoring the main process variables. Other experimental work included studies of the bed temperature and pressure profiles, the waste gas oxygen concentrations, unsymmetrical operation and supplying purge from different sources. The theoretical aims were to further develop the instantaneous local equilibrium (ILE) model used by Kirkby (1984). The model was made more efficient and developed to include novel options for waste recycling and the previously neglected, but common, design feature of supplying purge directly from one bed to another. The model's qualitative agreement with experiments was verified over a wider range of cycles and the quantitative agreement was improved for some cycles.

A new concept of a "fiber sorbent" has been investigated. The fiber sorbent is produced as a pseudo-monolithic material comprising polymer (cellulose acetate, CA) and zeolite (NaY) by applying hollow fiber spinning technology. Phase separation of the polymer solution provides an appropriately porous structure throughout the fiber matrix. In addition, the zeolite crystals are homogeneously dispersed in the polymer matrix with high loading. The zeolite is the main contributor to sorption capacity of the fiber sorbent. Mass transfer processes in the fiber sorbent module are analyzed for hydrogen recovery and compared with results for an equivalent size packed bed with identical diameter and length. The model indicates advantageous cases for application of fiber sorbent module over packed bed technology that allows system downsizing and energy saving by changing the outer and bore diameters to maintain or even reduce the pressure drop. The CA-NaY fiber sorbent was spun successfully with highly porous structure and high CO2 sorption capacity. The fiber sorbent enables the shell-side void space for thermal moderation to heat of adsorption, while this cannot be applied to the packed bed. The poly(vinyl alcohol) coated CA-NaY demonstrated the thermal moderation with paraffin wax, which was carefully selected and melt at slightly above operating temperature, in the shell-side in a rapidly cycled pressure swing adsorption. So this new approach is attractive for some hydrogen recovery applications as an alternative to traditional zeolite pellets.

This thesis is concerned with the design, operation and control of pressure swing adsorption (PSA) systems, employing state of the art system engineering tools. A detailed mathematical model is developed which captures the hydrodynamic, mass transfer and equilibrium effects in detail to represent the real PSA operation. The first detailed case study presented in this work deals with the design of an explicit/multi-parametric model predictive controller for the operation of a PSA system comprising four adsorbent beds undergoing nine process steps, separating 70 % H2, 30 % CH4 mixture into high purity hydrogen. The key controller objective is to fast track H2 purity to a set point value of 99.99 %, manipulating time duration of the adsorption step, under the effect of process disturbances. To perform the task, a rigorous and systematic framework is employed comprising four main steps of model development, system identification, the mp-MPC formulation, and in-silico closed loop validation, respectively. Detailed comparison studies of the derived explicit MPC controller are also performed with the conventional PID controllers, for a multitude of disturbance scenarios. Following the controller design, a detailed design and control optimization study is presented which incorporates the design, operational and control aspects of PSA operation simultaneously, with the objective of improving real time operability. This is in complete contrast to the traditional approach for the design of process systems, which employs a two step sequential method of first design and then control. A systematic and rigorous methodology is employed towards this purpose and is applied to a two-bed, six-step PSA system represented by a rigorous mathematical model, where the key optimization objective is to maximize the expected H2 recovery while achieving a closed loop product H2 purity of 99.99 %, for separating 70 % H2, 30 % CH4 feed. Furthermore, two detailed comparative studies are also conducted. In the first study, the optimal design and control configuration obtained from the simultaneous and sequential approaches are compared in detail. In the second study, an mp-MPC controller is designed to investigate any further improvements in the closed loop response of the optimal PSA system. The final area of research work is related to the development of an industrial scale, integrated PSA-membrane separation system. Here, the key objective is to enhance the overall recovery of "fuel cell ready" 99.99 % pure hydrogen, produced from the steam methane reforming route, where PSA is usually employed as the purification system. In the first stage, the stand-alone PSA and membrane configurations are optimized performing dynamic simulations on the mathematical model. During this procedure, both upstream and downstream membrane configuration are investigated in detail. For the hybrid configuration, membrane area and PSA cycle time are chosen as the key design parameters. Furthermore, life cycle analysis studies are performed on the hybrid system to evaluate its environmental impact in comparison to the stand-alone PSA system.

Carbon capture and storage technologies (CCS) are expected to play a key role in the future energy matrix. Different gas separation processes are under investigation with the purpose of becoming a more economical alternative than solvent based post combustion configurations. Previous works have proved that pressure swing adsorption (PSA) cycles manage to reach similar carbon capture targets than conventional amine process but with approx. a 50% lower specific energy consumption when they are applied at lab scale. These encouraging results suggest that research must be undertaken to study the feasibility of this technology at a low to medium power plant scale. The simulation of PSA cycles is a computationally challenging and time consuming task that requires as well a large set of experimentally measured data as input parameters. The assumption of Equilibrium Theory reduces the amount of empirically determined input variables that are necessary for modelling adsorption dynamics as well as enabling a simpler code implementation for the simulators. As part of this work, an Equilibrium Theory PSA cycle solver (Esim) was developed, the novel tool enables the quantification of the thermodynamic limit for a given PSA cycle allowing as well a pre-selection of promising operating conditions and configurations (high separation efficiency) for further investigation by using full governing equation based software The tool presented in this thesis is able to simulate multi-transition adsorption systems that obey any kind of equilibrium isotherm function without modifying its main code. The second part of this work is devoted to the design, simulation and optimisation of two stage two bed Skarmstrom PSA cycles to be applied as a pre-combustion process in a biomass gasification CHP plant. Simulations were carried out employing an in house software (CySim) in which full governing equations have been implemented. An accurate analysis of the operating conditions and cycle configurations was undertaken in order to improve the performance of the carbon capture unit. It was estimated that the energy penalty associated with the incorporation of the adsorptive pre combustion process was lower for a conventional post combustion solvent unit, leading as well to lower specific energy consumption per unit of captured CO2 and higher overall efficiencies for the CHP plant with installed pre-combustion PSA cycles. This work is pioneer in its kind as far as modelling, simulation, optimisation and integration of PSA units in energy industries is concerned and its results are expected to contribute to the deployment of this technology in the future energy matrix.

In this work, a dynamic mathematical model was developed for the simulation of the pressure swing adsorption process (PSA), through the Aspen Adsorption software for the purpose of validation, optimisation, and control of the nitrogen generation in the PSA pilot plant located at the Fachhochschule Münster (Münster University of Applied Sciences), Faculty of Chemical Engineering - Steinfurt. The mathematical model for the description of the transport phenomena developed within the packed column filled by adsorbent material (CMS) was formulated through the application of several assumptions in the mass/momentum and energy balances, in order to generate inside the software a correct set of partial differential equations. Simulation studies were performed to investigate the effect of changing various process variables such as the duration of PSA cycle time, the heat effect, and pressure drop, in order to achieve higher purity (up to 10 ppm of residual oxygen). A comparison between simulation results of a dynamic model and experimental results were carried out to evaluate selected assumptions. The outcome showed that the model is reliable in some purity intervals while it is not entirely satisfactory when high purity is required (99.999 % nitrogen) because data for a detailed description of kinetics or transport phenomena are missing. Other possible reasons and future improvements were discussed at the end of this work.

L’azoto è uno dei prodotti principali dell’industria chimica, utilizzato principalmente per assicurare un sicuro stoccaggio di composti infiammabili. Generatori con sistemi PSA sono spesso più economici della tradizionale distillazione criogenica. I processi PSA utilizzano una colonna a letto fisso, riempita con materiale adsorbente, che adsorbe selettivamente un componente da una miscela gassosa. L’ossigeno diffonde molto più velocemente dell'azoto nei pori di setacci molecolari carboniosi. Oltre ad un ottimo materiale adsorbente, anche il design è fondamentale per la performance di un processo PSA. La fase di adsorbimento è seguita da una fase di desorbimento. Il materiale adsorbente può essere quindi riutilizzato nel ciclo seguente. L’assenza di un simulatore di processo ha reso necessario l’uso di dati sperimentali per sviluppare nuovi processi. Un tale approccio è molto costoso e lungo. Una modellazione e simulazione matematica, che consideri tutti i fenomeni di trasporto, è richiesta per una migliore comprensione dell'adsorbente sia per l'ottimizzazione del processo. La dinamica della colonna richiede la soluzione di insiemi di PDE distribuite nel tempo e nello spazio. Questo lavoro è stato svolto presso l'Università di Scienze Applicate - Münster, Germania. Argomento di questa tesi è la modellazione e simulazione di un impianto PSA per la produzione di azoto con il simulatore di processo Aspen Adsorption con l’obiettivo di permettere in futuro ottimizzazioni di processo affidabili, attendibili ed economiche basate su computazioni numeriche. E' discussa l’ottimizzazione di parametri, dati cinetici, termodinamici e di equilibrio. Il modello è affidabile, rigoroso e risponde adeguatamente a diverse condizioni al contorno. Tuttavia non è ancora pienamente soddisfacente poiché manca una rappresentazione adeguata della cinetica ovvero dei fenomeni di trasporto di materia. La messa a punto del software permetterà in futuro di indagare velocemente nuove possibilità di operazione.

Equilibrium adsorption properties are studied on zeolites for the application of upgrading biogas from landfills. Pure adsorption isotherms of carbon dioxide (CO2) and methane (CH4) measured with a constant volume apparatus. The Henry's Law constant and the heat of adsorption for NaLSX is also determined. The adiabatic working capacity and selectivity of four adsorbents is compared. NaLSX showed the highest capacity for CO2 at elevated temperatures. The binary equilibrium of CO2/CH4 on NaLSX is measured in a modified gas chromatograph at total mixture pressures of 1 and 3.3 atmospheres. The adsorbed phase is dominated by CO2 with a selectivity of 20 to 100 for the separation of CO2 and CH4. The increase in total pressure resulted in an increase in adsorbent capacity and a decrease in selectivity. Finally, an economic analysis relates landfill size to PSA operational costs and returns.

Pressure Swing Adsorption (PSA) is the most efficient option for middle scale separation processes. PSA is a cyclic process whose main steps are adsorption, at high pressure, and regeneration of the adsorbent, at low pressure. The design of PSA cycles is still mainly approached experimentally due to the computational challenges posed by the complexity of the simulation and by the need to detect the performance at cyclic steady state (CSS). Automated tools for the design of PSA processes are desirable to allow a better understanding of the the complex relationship between the performance and the design variables. Furthermore, the operation is characterised by trade-offs between conflicting criteria. A multi-objective flowsheet design framework for complex PSA cycles is presented. A suite of evolutionary procedures, for the generation of alternative PSA configurations has been developed, including simple evolution, simulated annealing as well as a population based procedure. Within this evolutionary procedure the evaluation of each cycle configuration generated requires the solution of a multi-objective optimisation problem which considers the conflicting objectives of recovery and purity. For this embedded optimisation problem a multi-objective genetic algorithm (MOGA), with a targeted fitness function, is used to generate the approximation to the Pareto front. The evaluation of each alternative design makes use of a number of techniques to reduce the computational burden. The case studies considered include the separation of air for N2 production, a fast cycle operation which requires a detailed diffusion model, and the separation of CO2 from flue gases, where complex cycles are needed to achieve a high purity product. The novel design framework is able to determine optimal configurations and operating conditions for PSA for these industrially relevant case studies. The results presented by the design framework can help an engineer to make informed design decisions.

Pressure swing adsorption (PSA) is a cyclic adsorption process for gas separation and purification, and can be used in a variety of industrial applications, for example, hydrogen purification and dehydration. PSA is, due to its low operational cost and its ability to efficiently separate CO2 from flue gas, a promising candidate for post-combustion carbon capture in power plants, which is an important link in the Carbon Capture and Storage technology chain. PSA offers many design possibilities, but to optimise the performance of a PSA system over a wide range of design choices, by experimental means, is typically too costly, in terms of time and resources required. To address this challenge, computer experiments are used to emulate the real system and to predict the performance. The system of PDAEs that describes the PSA process behaviour is however typically computationally expensive to simulate, especially as the cyclic steady state condition has to be met. Over the past decade, significant progress has been made in computational strategies for PSA design, but more efficient optimisation procedures are needed. One popular class of optimisation methods are the Evolutionary algorithms (EAs). EAs are however less efficient for computationally expensive models. The use of surrogate models in optimisation is an exciting research direction that allows the strengths of EAs to be used for expensive models. A surrogate based optimisation (SBO) procedure is here developed for the design of PSA systems. The procedure is applicable for constrained and multi-objective optimisation. This SBO procedure relies on Kriging, a popular surrogate model, and is used with EAs. The main application of this work is the design of PSA systems for CO2 capture. A 2- bed/6-step PSA system for CO2 separation is used as an example. The cycle configuration used is sufficiently complex to provide a challenging, multi-criteria example.

Strong dependency on fossil fuels and the associated price and supply chain risk increase the need for more efficient utilisation of existing non-renewable energy sources. Carbon capture and hydrogen purification technologies are expected to play a key role in the future low-carbonised energy matrix. Integrated Gasification Combined Cycles (IGCCs) are one of the emerging clean coal technologies which pave the way for producing power from coal with a higher net power efficiency than conventional PC-fired boiler power plants. It is also advantageous that in an IGCC power plant a carbon capture unit can be applied to a stream having a very high CO2 partial pressure ahead of gas combustion that would not be available in case of a PC-fired boiler power plant, leading to less energy penalty involved in carbon capture. At the same time, the production of ultrapure hydrogen is both a sought target and an appropriate environmental solution because it is commonly utilised as feedstock in refineries’ hydrotreaters and hydrocrackers as well as energy carrier in fuel cells. A high purity of hydrogen has been commercially produced out of raw synthesis gas using a Hydrogen Pressure Swing Adsorption (H2 PSA) process. In this thesis, it was aimed to design and optimise a bespoke H2 PSA system tailored for a decarbonised syngas feed originating from a carbon capture unit. Therefore, a novel H2 PSA has been studied that is applied to an advanced IGCC plant for cogenerating power and ultrapure hydrogen (99.99+ mol%) with pre-combustion CO2 capture. In designing the H2 PSA, it is essential to increase the recovery of ultrapure hydrogen product to its maximum since the power consumption for compressing the H2 PSA tail gas up to the gas turbine operating pressure should be minimised to save the total auxiliary power consumption. Hydrogen recovery was raised by increasing the complexity of the PSA step configuration that allows a PSA cycle to have a lower feed flow to one column being used for adsorption and more pressure equalisation steps. An in-depth economic analysis was carried out and discussed in detail. The industrial advanced IGCC performances have also been improved by process integration between the H2 PSA unit and other units in the plant.

The topic of this master thesis is upgrading of biogas. As a mixture of gases produced during anaerobic digestion, contains methane which is highly energy valuable gas. But also other substances that we want to remove. We will present the motivation for upgrading biogas and the possibility of separation, generally the pressure swing adsorption method. The key parameter of this technique is the choice of a suitable adsorbent. This is possible based on the knowledge of adsorption processes, therefore, is also described below. The objective of this thesis is to determine the parameters of the pressure swing adsorption metod. To do this it is necessary to determine the adsorption capacity of the adsorbent, measure breakthrough curves of carbon dioxide and methane, and determine the pressure drop of solid bed, etc. As a result we can finally make a balance and evaluate the applicability in practice.

L'objet de ce travail est la conception, l'étude et le dimensionnement d'opérations multicolonnes et multiadsorbants. Le travail présenté est surtout de nature méthodologique: il s'agit de développer et de tester des nouveaux outils et des nouvelles méthodes ayant un caractère assez géneral. Néanmoins, l'ensemble de cette étude s'appuiera sur une application proposée par le partenaire industriel de cette recherche: il s'agit de la production d'hydrogène pur par adsorption modulée en pression (PSA), à partir de gaz de cracking du gaz naturel. On a développé les modèles mathématiques utilisés pour simuler le procédé PSA ainsi que les méthodes de résolution adéquates. La description du logiciel de simulation PSASIM et ses différentes fonctionnalités sont illustrées par un exemple de procédé à 6 étapes et 2 colonnes. On a utilise PSASIM pour déterminer la longueur des couches d'adsorbant et la durée des étapes isobares. La caractérisation du fonctionnement global d'un procédé PSA est développée dans le dernier chapitre. On spécifie les différents critères de performance à étudier ainsi que les paramètres influents. On y développe deux démarches: plan d'expériences et réseau de neurones, qui conduisent à des polynômes ou des procédures simples donnant les performances en fonction des paramètres opératoires

The thesis deals with the technologies upgrading the biogas to the quality of the natural gas for the following use in the gas distribution system. The main concern of the thesis is the pressure swing adsorption (PSA), which is nowadays one of the most exploited technologies. For a certain flow and composition of the biogas, completely new PSA technology was designed. Technological schema was created and the main technological devices (adsorbers) were drawn up together with the design documentation for this new technology. The important part of the thesis is also the model of the whole PSA technology in the ChemCAD programme and the evaluation of the operating and investment costs.

El continu increment en l'ús de les energies renovables i els objectius per a la reducció de les emissions de diòxid de carboni (CO2) requereixen canvis significatius tant a nivell tècnic com a nivell normatiu. La captura i utilització de diòxid de carboni (CCU, per les sigles en anglès) és un mètode eficaç per aconseguir la mitigació del CO2 i al mateix temps mantenir de forma segura els subministraments d'energia. Si bé la demanda a la reducció de les emissions de CO2 està augmentant, l'eficiència energètica i el cost dels processos de captura de CO2 segueixen sent un factor limitant per a les aplicacions industrials. En el present treball s'estudia l'ús del procés d'adsorció per oscil·lació de pressió i buit (VPSA, per les sigles en anglès) amb adsorbents d'alta selectivitat per separar el CO2 dels gasos de combustió, com un mètode alternatiu al procés d'absorció tradicional amb amines. Es realitza un estudi preliminar mitjançant Anàlisi Tèrmica per determinar la capacitat d’adsorció i el comportament cíclic de la captura de CO2 per deu adsorbents comercials, inclosos els tamisos moleculars de carboni (CMS) i les zeolites. L'anàlisi es va fer amb CO2 pur, N2 pur i mescles dels dos gasos en la proporció 15%/85% que correspon a la composició d’un gas de combustió normal; s’usen les zeolites comercials 13X, 5A, 4A sense i amb aglomerants i tres tamisos moleculars de carboni (CMS) en l’interval de pressió de 0 a 10 bar i a 283K, 298K, 232K i 323 K de temperatura. Els resultats s’han ajustat amb els models Toth, Sips i Dual Site Langmuir (DSL). Es va realitzar una selecció entre deu adsorbents comercials per a la captura de CO2, inclosos els tamisos moleculars de carbó (CMS, per les sigles en anglès) i les zeolites. Es van determinar les propietats texturals, la capacitat d'adsorció i el comportament cíclic dels adsorbents per comparar el seu comportament a la separació del diòxid de carboni del nitrogen. Posteriorment, es van mesurar les isotermes d'adsorció d'un sol component en la balança de suspensió magnètica a quatre temperatures diferents (283, 298, 232 i 323 K) i en un ampli marge de pressions (de 0 a 10 bara). Les dades sobre les isotermes de components purs es van correlacionar utilitzant els models Toth, Sips i Dual Site Langmuir (DSL). Es van dissenyar i construir tres unitats de laboratori per realitzar l'experimentació del procés VPSA. La primera unitat es va usar per a la producció i el control de mescles gasoses de CO2 i N2 a una pressió màxima de 9 bara. En la segona unitat es van dur a terme la determinació dels equilibris d'adsorció amb una barreja de composició semblant a la dels gasos de combustió (15/85% de CO2/N2 v/v). Amb el programa Aspen Adsorption® es va simular el sistema experimental, obtenint que les prediccions del model DSL reprodueixen suficientment bé els resultats experimentals de les corbes de ruptura i els perfils de temperatura en el llit fix. A més, es van fer estudis dinàmics per avaluar les zeolites 5ABL i 13XBL usant el procés VPSA discontinu per a la separació CO2 de N2. La unitat dos es va dotar d'un sistema de control amb una interfície PLC que facilita la seva operació i automatització, usant una estratègia de control desenvolupada en aquest treball. En base als resultats obtinguts amb la unitat dos, tant experimentals com simulats, es va trobar que la zeolita 13XBL era la més adequada per al procés VPSA proposat. Els resultats experimentals es van emprar per alimentar el disseny de la unitat dos a Aspen Adsorption® i validar el model usat que al seu torn es va utilitzar per realitzar un disseny complet d'experiències de dos factors (26) en configuració continua. La tercera unitat experimental consta de tres columnes d'adsorció on es va incloure l'estratègia de control desenvolupada per la unitat dos i es va incloure la recirculació dels corrents rics en N2 i CO2. Es van dur a terme tres experiments del procés VPSA cíclic de 8 passos canviant els paràmetres de control del procés automatitzat i usant la zeolita 13XBL com adsorbent. Es va aconseguir satisfer els objectius en termes puresa de CO2 (> 80%) i consum energètic (<2.5 kWh/kgCO2). Sobre la base dels resultats experimentals i simulats, es va realitzar una demostració a escala pilot de la captura de CO2 del gas de combustió d'una caldera de vapor en una planta industrial a situada a la província de Barcelona.La planta pilot de captura de CO2 consta d'un procés de pretractament dels gasos de combustió, una unitat VPSA acoblada amb una unitat de deshumidificació i una aplicació industrial per a l'ús del CO2. A la unitat de pretractament, els gasos de combustió es van refredar de 70ºC a 25ºC i es van desnitrificar. A la unitat de deshumidificació, es va eliminar el vapor d'aigua del gas desnitrificat mitjançant adsorció sobre alúmina. Posteriorment, es va emprar el procés VPSA de vuit passos amb tres columnes usant zeolita 13XBL, en la qual es va obtenir un corrent enriquit de CO2 de 85 a 95% de puresa de CO2, amb una recuperació del 48 a 56%, una productivitat de 0,20-0,25 gCO2/(gads·h) i un consum energètic de 1.48 kWh/kgCO2. El CO2 recuperat es va usar per reemplaçar l'ús d'àcids minerals en l'etapa de regulació del pH de la planta de tractament d'aigües residuals existent a la fàbrica. Per tant, el procés desenvolupat és una alternativa efectiva per separar el CO2 dels punts d'emissió de gasos de combustió industrial i utilitzar el CO2 recuperat com a matèria primera per a aplicacions industrials. L'ús de CO2 capturat en aquestes fonts d'emissió té dos avantatges clars. D'una banda, es van reduir les emissions de CO2 a la atmosfera. De l'altra, va permetre reutilitzar i transformar un contaminant ambiental en compostos neutres.
El continuo incremento en el uso de las energías renovables y los objetivos para la reducción de las emisiones de dióxido de carbono (CO2) requieren cambios significativos tanto a nivel técnico como a nivel normativo. La captura y utilización de dióxido de carbono (CCU, por sus siglas en inglés) es un método eficaz para lograr la mitigación del CO2 y al mismo tiempo mantener de forma segura los suministros de energía. Si bien la demanda en la reducción de las emisiones de CO2 está aumentando, la eficiencia energética y el costo de los procesos de captura de CO2 siguen siendo un factor limitante para las aplicaciones industriales. En el presente trabajo se estudia el uso del proceso de adsorción por oscilación de presión y vacío (VPSA, por sus siglas en inglés) con adsorbentes de alta selectividad para separar el CO2 de los gases de combustión, como un método alternativo al proceso de absorción tradicional con aminas. Se realizó una selección entre diez adsorbentes comerciales para la captura de CO2, incluidos los tamices moleculares de carbón (CMS, por sus siglas en inglés) y las zeolitas. Se determinaron las propiedades texturales, la capacidad de adsorción y el comportamiento cíclico de los adsorbentes para comparar su comportamiento en la separación del dióxido de carbono del nitrógeno. Posteriormente, se midieron las isotermas de adsorción de un solo componente en la balanza de suspensión magnética a cuatro temperaturas diferentes (283, 298, 232 y 323 K) y en un amplio margen de presiones (de 0 a 10 bara). Los datos sobre las isotermas de componentes puros se correlacionaron utilizando los modelos Toth, Sips y Dual Site Langmuir (DSL). Se diseñaron y construyeron tres unidades de laboratorio para realizar la experimentación del proceso VPSA. La primera unidad se usó para la producción y el control de mezclas gaseosas de CO2 y N2 a una presión máxima de 9 bara. En la segunda unidad se llevaron a cabo las mediciones de los equilibrios de adsorción con una mezcla de composición semejante a la de los gases de combustión (15/85% de CO2/N2 v/v). Con el programa Aspen Adsorption® se simuló el sistema experimental, obteniendo que las predicciones del modelo DSL reproducen suficientemente bien los resultados experimentales de las curvas de ruptura y los perfiles de temperatura en el lecho fijo. Además, se hicieron estudios dinámicos para evaluar las zeolitas 5ABL y 13XBL usando el proceso VPSA discontinuo para la separación CO2 de N2. La unidad dos se dotó de un sistema de control con una interfaz PLC que facilita su operación y automatización, usando una estrategia de control desarrollada en este trabajo. En base a los resultados obtenidos con la unidad dos y su simulación, se encontró que la zeolita 13XBL era la que la más adecuada para el proceso VPSA propuesto. Los resultados experimentales se usaron para alimentar el diseño de la unidad dos en Aspen Adsorption® y validar el modelo usado que a su vez se utilizó para realizar un diseño completo de experiencias de dos factores (26) en configuración discontinua. La tercera unidad experimental consta de tres columnas de adsorción donde se incluyó la estrategia de control desarrollada para la unidad dos y se incluyó la recirculación de las corrientes ricas en N2 y CO2. Se llevaron a cabo tres experimentos en el proceso VPSA cíclico de 8 pasos cambiando los parámetros de control del proceso automatizado y usando la zeolita 13XBL como adsorbente. Se logró satisfacer los objetivos en términos pureza de CO2 (>80%) y consumo energético (<2.5 kW·h/kgCO2). Sobre la base de los resultados experimentales y simulados, se realizó una demostración a escala piloto de la captura de CO2 del gas de combustión de una caldera de vapor en una planta industrial situada en la provincia de Barcelona. La planta piloto de captura de CO2 consta de un proceso de pretratamiento de los gases de combustión, una unidad VPSA acoplada con una unidad de deshumidificación y una aplicación industrial para el uso del CO2. En la unidad de pretratamiento, los gases de combustión se enfriaron de 70ºC a 25ºC y desnitrificaron. En la unidad de deshumidificación, se eliminó el vapor de agua del gas desnitrificado mediante adsorción con alúmina. Posteriormente, se empleó el proceso VPSA de ocho pasos con tres columnas usando zeolita 13XBL, en la que se obtuvo una corriente enriquecida de CO2 de 85 a 95% de pureza de CO2, con una recuperación del 48 a 56%, una productividad de 0.20 a 0.25 gCO2/(gads٠h-) y un consumo energético de 1.48 kWh/ kgCO2. El CO2 recuperado se usó para reemplazar el uso de ácidos minerales en la etapa de regulación del pH de la planta de tratamiento de aguas residuales existente en la fábrica. Por lo tanto, el proceso desarrollado es una alternativa efectiva para separar el CO2 de los puntos de emisión de gases de combustión industrial y utilizar el CO2 recuperado como materia prima para aplicaciones industriales. El uso de CO2 capturado en estas fuentes de emisión tiene dos ventajas claras. Por un lado, redujeron las emisiones de CO2 a la atmósfera. Por otro lado, permitió reutilizar y transformar un contaminante ambiental en compuestos neutros.
The continuously increasing share of renewable energy sources and European Union targets for carbon dioxide (CO2) emission reduction need significant changes both on a technical and regulatory level. Carbon dioxide capture and utilization (CCU) is an effective method for achieving CO2 mitigation while simultaneously keeping energy supplies secure. While the demand for reduction in CO2 emissions is increasing, the improvement of energy-efficiency and the cost of CO2 capture processes remains a limiting factor for industrial applications. The present work studies the Vacuum Pressure Swing Adsorption process (VPSA) using high selectivity adsorbents for separating CO2 from flue gas as an alternative method to the traditional absorption process with amines. A screening analysis for CO2 capture was conducted on ten commercial adsorbents, including carbon molecular sieves (CMS) and zeolites. The textural properties, the adsorption capacities and the adsorbent cyclic behaviors were determined to compare their performance in the context of CO2 separation from nitrogen (N2). Subsequently, the single component adsorption isotherms were measured in a magnetic suspension balance at four different temperatures (283, 298, 232 and 323 K) and over a large range of pressures (from 0 to 10 bara). Data on the pure component isotherms were correlated using the Toth, Sips and Dual Site Langmuir (DSL) models. Three laboratory units were designed and built to perform the VPSA experiments. The first was used for the production and control of CO2 and N2 gas mixtures at a maximum pressure of 9 bara. Adsorption equilibrium measurements with a mixture that resembles the composition of combustion gases (15/85% CO2/N2 v/v) were obtained using the second unit that was built. Afterwards, the Aspen Adsorption® program was used to simulate the experimental system, where the predictions of the DSL model agree with the breakthrough curves and the temperature profiles of the experimental fixed bed results. In addition, dynamic studies were performed to evaluate the zeolites 5ABL and 13XBL using a discontinuous VPSA process for the CO2 separation of N2. The process was automated and operated with a PLC interface, using a control strategy developed in this work. Based on the comparison results of the zeolites, it was found that the 13XBL zeolite was the one most suitable for the proposed VPSA process. The experimental results were verified by numerical simulations in the Aspen Adsorption® software and the validated model was used to perform a two-factor complete design of experiments (26) using 13XBL simulations in a discontinuous configuration. The third experimental unit was built with three adsorption columns which included the developed control strategy and the recirculation of N2 and CO2 rich streams. Three experiments were carried out using zeolite 13XBL as an adsorbent for the proposed 8-step VPSA cyclic process by changing the control parameters of the automated process. Through the experiments, the objectives were achieved in terms of CO2 purity (> 90%) and energy consumption (> 2.5 kWh/kgCO2). Based on the experimental and simulated results, a pilot-scale demonstration plant for CO2 capture from flue gas in an existing industrial boiler in a Spanish company was carried out. The pilot-scale CO2 capture plant consisted of a pre-treatment process for flue gases, a VPSA unit coupled with a dehumidification unit and an industrial application for the use of CO2. In the pretreatment unit the flue gases were cooled from 70°C to 25°C and then denitrified. In the dehumidification unit, the water vapor was removed from the denitrified gas by adsorption with alumina. Subsequently, the three columns’ eight-step VPSA process developed with zeolite 13XBL was used. The results were a product purity of 85 to 95% of CO2, a recovery of 48 to 56%, a productivity of 0.20 to 0.25 gCO2/(gads٠h) and an energy consumption of 1.48 kWh/kgCO2. The recovered CO2 was then used to replace the use of mineral acids in the pH regulation stage of the existing wastewater treatment plant. Therefore, it is concluded that the developed process is an effective alternative to separate the CO2 from the emission points of industrial combustion gases and to use the recovered CO2 as raw material for industrial applications. The use of CO2 captured in these emission sources has two clear advantages. On the one hand, it reduces the CO2 emissions to the atmosphere. On the other hand, it allows the reuse and transformation of an environmental pollutant into neutral compounds.

Cette étude concerne les procédés d'adsorption de gaz pour lesquels la régénération de l'adsorbant est effectuée principalement par augmentation de la température. Les adsorbants sont des tamis moléculaires et les gaz utilisés expérimentalement sont essentiellement des alcanes et du dioxyde de carbone. En vue de modéliser de tels procédés, on effectue une description détaillée des différents phénomènes impliqués. Ainsi, on propose des modèles thermodynamiques pour décrire les équilibres multiconstituants gaz-solide à partir de mesures des isothermes des gaz purs ou de mesures de perturbations chromatographiques, ainsi que les méthodes expérimentales associées. On considère que le transfert de matière gaz-solide est représenté par une diffusion interne au grain uniquement. Le transfert de chaleur est étudié tant au niveau du grain d'adsorbant qu'au niveau de la colonne pour laquelle on envisage les trois cas : isotherme, adiabatique et intermédiaire. On étudie également le cas d'un mélange contenant un gaz condensable. La résolution numérique des équations conduit à un logiciel de simulation. Les simulations réalisées permettent d'explorer l'influence des paramètres opératoires sur l'histoire des concentrations en sortie de colonne, en saturation et en régénération, notamment l'influence du transfert de matière, du transfert de chaleur gaz-adsorbant, des pertes de chaleur a la paroi, de la température du gaz de régénération dans le cas d'une espèce condensable.

An investigation was undertaken to determine the feasibility of increasing the hydrogen production rate by coupling the water gas shift (WGS) process to the hybrid sulphur process (HyS). This investigation also involved the technical and economical analysis of the water gas shift and the H2 separation by means of Pressure swing adsorption (PSA) process. A technical analysis of the water gas shift reaction was determined under the operating conditions selected on the basis of some information available in the literature. The high temperature system (HTS) and low temperature system (LTS) reactors were assumed to be operated at temperatures of 350ºC and 200ºC, respectively. The operating pressure for both reactors was assumed to be 30 atmospheres. The H2 production rate of the partial oxidation (POX) and the WGS processes was 242T/D, which is approximately two times the amount produced by the HyS process alone. The PSA was used for the purification process leading to a hydrogen product with a purity of 99.99%. From the total H2 produced by the POX and the WGS processes only 90 percent of H2 is recovered in the PSA. The unrecovered H2 leaves the PSA as a purge gas together with CO2 and traces of CH4, CO, and saturated H2O. The estimated capital cost of the WGS plant with PSA is about US$50 million. The production cost is highly dependent on the cost of all of the required raw materials and utilities involved. The production cost obtained was US $1.41/kg H2 based on the input cost of synthesis gas as produced by the POX process. In this case the production cost of synthesis gas based on US $6/GJ for natural gas and US $0/Ton for oxygen was estimated to be US $0.154/kg. By increasing the oxygen and natural gas cost, the corresponding increase in synthesis gas has resulted in an increase in H2 production cost of US $1.84/kg.
Thesis (M.Sc. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2006.

An investigation was undertaken to determine the feasibility of increasing the hydrogen production rate by coupling the water gas shift (WGS) process to the hybrid sulphur process (HyS). This investigation also involved the technical and economical analysis of the water gas shift and the H2 separation by means of Pressure swing adsorption (PSA) process. A technical analysis of the water gas shift reaction was determined under the operating conditions selected on the basis of some information available in the literature. The high temperature system (HTS) and low temperature system (LTS) reactors were assumed to be operated at temperatures of 350°C and 200°C, respectively. The operating pressure for both reactors was assumed to be 30 atmospheres. The H2 production rate of the partial oxidation (POX) and the WGS processes was 242T/D, which is approximately two times the amount produced by the HyS process alone. The PSA was used for the purification process leading to a hydrogen product with a purity of 99.99%. From the total H2 produced by the POX and the WGS processes only 90 percent of H2 is recovered in the PSA. The unrecovered H2 leaves the PSA as a purge gas together with C02 and traces of CH4, CO, and saturated H20. The estimated capital cost of the WGS plant with PSA is about US$50 million. The production cost is highly dependent on the cost of all of the required raw materials and utilities involved. The production cost obtained was US $1.41/kg H2 based on the input cost of synthesis gas as produced by the POX process. In this case the production cost of synthesis gas based on US $6/GJ for natural gas and US $0/Ton for oxygen was estimated to be US $0.154/kg. By increasing the oxygen and natural gas cost, the corresponding increase in synthesis gas has resulted in an increase in H2 production cost of US $1.84/kg.
Thesis (M.Sc. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2009.

Dans cette thèse, nous nous intéressons à la modélisation, la simulation et la commande d'un procédé d'adsorption modulée en pression (procédé PSA). Ces procédés PSA sont des procédés cycliques alternant phase d'adsorption et phase de désorption. Les modèles de ces procédés sont en général décrits par des équations au dérivées partielles qui suivant les modèles décrivent les dynamiques lentes et rapides. Nous avons étudié la modélisation d'un procédé basé sur deux colonnes avec l'utilisation d'un adsorbant monodisperse. Nous proposons un modèle classique qui décrit les quatre phases du cycle du procédé sur chacune des colonnes ainsi qu'un modèle continu équivalent à contre courant. Le premier modèle aboutit à quatre systèmes d'équations aux dérivées partielles décrivant les bilans de matière sur les colonnes pour chaque phase du cycle. Le second modèle, valide pour des temps de cycle faibles, aboutit à un seul système d'équations aux dérivées partielles. Nous nous sommes aussi intéressés à la réduction spatiale des modèles de colonne décrits par des systèmes hamiltoniens à ports de dimension infinie. Nous avons montré que le spectre de tels systèmes peut être déduit du spectre associé à une structure canonique, la structure de Stockes Dirac, à l'aide de transformations géométriques simples. En particulier, nous avons montré sur un modèle simple de colonne d'adsorption admettant une solution analytique pour son calcul de spectre, qu'une méthode de discrétisation structurée de type éléments finis mixtes fournit un spectre discrétisé plus proche du spectre de l'opérateur initial qu'une méthode de discrétisation par différence finie. Cette méthode structurée de discrétisation conserve la structure d'interconnexion des échanges de puissance à l'intérieur du système et à ses frontières. Nous avons enfin proposé une synthèse de loi de commande robuste du procédé P.S.A. basée sur un modèle de Hammerstein identifié à partir du modèle classique entre la commande, le ratio entre durée d'adsorption et de désorption et la pureté du produit en sortie de procédé. Ce modèle moyenné sur un cycle est décrit par une dynamique linéaire avec retard et un gain statique non linéaire. Nous avons mis en œuvre des techniques de synthèse H1 dans le domaine fréquentiel en utilisant la factorisation J-spectrale. Les performances du contrôleur sont bonnes en présence de perturbations sur la composition du mélange en entrée. Une comparaison de performance de commande avec la commande proportionnelle intégrale est aussi proposée
In this thesis, we focus on modeling, simulation and control of pressure swing adsorption processes (PSA). These PSA processes are cyclic since adsorption phase and desorption phase alternate. These models are usually described by partial differential equations and present fast dynamics and slow dynamics. We study the modeling of a process based on two columns with the use of an monodisperse adsorbent.We propose a classical model that describes the four phases of a cycle of the process on each column and an equivalent continuous countercurrent model. The first model leads to four systems of partial differential equations describing mass balances on the columns for each phase of the cycle. The second model results in a single system of partial differential equations valid for small cycle time. We are also interested in the spatial reduction of column models described by port Hamiltonian formulation of infinite dimensional system. We have shown that the spectrum of such systems can be deduced from the spectrum associated with a canonical structure, the Dirac Stokes structure, using simple geometric transformations. In particular, on a simple model of adsorption column admitting an analytical solution for the calculation of the spectrum, we show that the spectra obtained from a structured discretization method is closer to the original operator spectrum than the one obtained from the finite difference method. This structured discretization method preserves the structure of the interconnection of power exchanges within the system and its borders. We finally proposed a synthesis of robust control law of the PSA process based on a Hammerstein model identified from the classical model between the control, the ratio between the duration of adsorption and desorption and the purity of the product at the output of process. The averaged model over a cycle is described by a linear dynamics with delay and a nonlinear static gain. We have implemented the synthesis of H1 control in the frequency domain using J-spectral factorization. The performance of controller is good with the disturbance on the input composition. A comparison of control performance with proportional integral (PI) control is also proposed

La présente étude concerne l'étude exergétique des pompes à chaleur à absorption opérant par rectification inverse et des opérations d'adsorption modulée en pression. L’étude du diagramme température-enthalpie permet de mettre en évidence l'intérêt des divers types de pompe à chaleur à absorption présentes. L’analyse exergétique de la distillation permet de déterminer un optimum opératoire dépendant des conditions thermodynamiques du flux d'alimentation à séparer. La représentation d'un cycle de séparation - mélangeage sur un ensemble de diagrammes thermodynamiques permet de distinguer et de mesurer les flux de matière, d'enthalpie et d'exergie traversant le système. Sachant que la chaleur latente d'évaporation de tout corps pur s'annule au point critique, la réduction à zéro de la chaleur couteuse à fournir au système permet d'obtenir un coefficient de performance élevé. Comme pour la distillation, l'analyse exergétique des opérations d'adsorption modulée en pression permet de déterminer un optimum opératoire, montrant ainsi l'intérêt d'une telle approche

A mesure que l'intérêt mondial pour les énergies renouvelables s'intensifie, la production de biogaz ne cesse de croître, car elle est une source renouvelable et propre. La technologie de séparation par adsorption modulée en pression (Pressure Swing Adsorption ou PSA) se présente alors comme une des technologies intéressantes permettant la valorisation du biogaz en biométhane. La grande flexibilité du procédé PSA est liée en une certaine manière à sa complexité avec plusieurs paramètres de design et opératoires contrôlant les performances de l’unité de séparation. L’identification de ces paramètres par une approche expérimentale est pratiquement impossible et une phase d’étude numérique est primordiale pour dimensionner l’unité, concevoir le cycle de pression et déterminer les conditions optimales de fonctionnement, avant tout essai expérimental. L’objectif général de la thèse a été centré sur le développement d’outils de simulation d’un procédé de purification de biométhane par technologie PSA.Dans un premier temps, une simulation basée sur une modélisation dynamique monodimensionnelle non isotherme a été mise en place. Elle fait appel à un modèle cinétique d’adsorption de double force motrice (bi-LDF) pour décrire les échanges de matière intragranulaires. Le choix de l’adsorbant s’est porté sur un tamis moléculaire de carbone (CMS-3K) permettant d’assurer une grande sélectivité cinétique du dioxyde de carbone vis à vis du méthane (CH4). Le cycle PSA a été optimisé pour obtenir une récupération du CH4 de 92 % avec une consommation d'énergie spécifique modérée de 0,35 kWh/Nm3, tout en respectant les spécifications de pureté d’injection dans le réseau national (97 % de CH4). Les performances obtenues sont ainsi compatibles avec une exploitation industrielle. Ce cycle est composé de cinq colonnes et de quinze étapes incluant trois équilibrages et un recyclage de gaz de purge.Le développement d’un modèle numérique multidimensionnel (3D) et multi-échelle (colonne/grain/cristal) permettrait d’estimer les limites des hypothèses et des corrélations utilisées dans les simulateurs usuels. La première étape consiste à simuler l’écoulement du gaz dans un lit d’adsorbant ayant une morphologie la plus réaliste possible. Ainsi, lors de la seconde partie du travail de thèse, un lit constitué de billes inertes a été généré numériquement par calcul DEM (modélisation par éléments discrets) pour une colonne de taille de laboratoire. L’emploi d’OpenFOAM (logiciel CFD) a permis de calculer l’écoulement tridimensionnel d’un traceur dans la colonne. En parallèle une étude expérimentale du front de percée a été menée pour un lit de mêmes dimension et caractéristiques. Les temps de percée et les coefficients de dispersion-diffusion calculés et mesurés sont similaires. Cependant la simulation présente quelques divergences de la concentration du traceur localement dans la colonne, en raison de difficultés de maillage. L’étape suivante consistera à prendre en compte des interactions grains-fluide en considérant des grains poreux d’adsorbant
As global interest in renewable energy intensifies, biogas production continues to grow as a clean, renewable source. Pressure Swing Adsorption (PSA) is considered as one of the most interesting technologies for the valorization of biogas into biomethane. The great flexibility of the PSA process is linked in some way to its complexity with several design and operating parameters which control the performance of the separation unit. The identification of these parameters by an experimental approach is practically impossible. A numerical study stage is essential for sizing the unit, designing the pressure cycle and identifying the optimal operating conditions before any experimental test.The general objective of the thesis was focused on the development of simulation tools for a biomethane purification process using PSA technology.In a first stage, a simulation based on one-dimensional non-isothermal dynamic model, where the intragranular mass transfer kinetics was modelled using a double driving force (bi-LDF) approximation, was implemented. A carbon molecular sieve (CMS-3K) was selected. This adsorbent ensures a high kinetic selectivity of carbon dioxide with respect to methane (CH4). The optimized cycle, composed of five columns and fifteen steps including three equalization steps and a purge gas recycling allowed a CH4 recovery of 92% with a moderate specific energy consumption of 0.35 kWh/Nm3 , at the same time respecting the grid injection specifications (97% CH4 purity ). The performance obtained is thus compatible with industrial operation.The development of a multidimensional (3D) and multi-scale (column/grain/crystal) numerical model would serve to evaluate the limits of the assumptions and correlations used in usual simulators. The first step consists in simulating the gas flow in an adsorbent bed having a reaslistic stacking.. Thus, an inert packed bed was numerically generated by DEM calculation (discrete element modeling) for a column of laboratory size. The use of OpenFOAM (CFD software) allowed to calculate the three-dimensional tracer gas flow in the column. In parallel an experimental study of the breakthrough curves was carried out using a bed having the same dimensions and characteristics. The breakthrough times and the dispersion-diffusion coefficients calculated and measured were similar. However the simulation showed some divergences in the concentration of the tracer locally in the column, due to difficulties in meshing. The next step will consist in taking into account grain-fluid interactions by considering porous adsorbent grains

Pressure swing adsorption (PSA) is a widely applied technology for separating gases, which operates based on selective adsorption on solid adsorbents. Indeed, the demand of PSA process plants for nitrogen production on industrial scale is continuously growing, as consequence of the improvements achieved in terms of efficiency, competitiveness, and cost-effectiveness. In this work, the N2-PSA pilot plant located at the Münster University of Applied Sciences, was used as study-case for the drafting of the industrial-scale basic design package of the plant. Firstly, it was shown that it is acceptable to develop the basic design package of full-scale PSA system based on information obtained by operation of pilot-scale system. Subsequently, a detailed description of technical data of plant components has been given, according to the international and European standards in force. Therefore, it was possible to produce technical drawings of the plant, i.e. process flow diagram (PFD) and piping and instrumentation diagram (P&ID), along with the required datasheets and a preliminary plant layout. Eventually, a preliminary safety assessment of the system was carried out.

Le présent travail s'intéresse à la modélisation des procédés de séparation de gaz par adsorption modulée en pression (AMP). Toutes les étapes faisant partie des cycles AMP, à savoir, la saturation, la régénération, la compression, la décompression et l'équilibrage, sont étudiées en détail. Un effort notable a été consenti en vue d'évaluer tous les paramètres intervenant dans la modélisation. Les modèles élaborés tiennent compte des aspects hydrodynamique et cinétique (de transfert de matière et de chaleur). En ce qui concerne l'écoulement, les lois de Darcy et d'Ergun ainsi que d'autres modèles plus simples sont comparés. L’écart entre les résultats de simulation obtenus avec les diverses considérations est plus ou moins important suivant les conditions opératoires. C’est pourquoi une attention particulière devrait être accordée quant au choix de la relation à adopter pour caractériser l'écoulement. Plusieurs cinétiques diffusionnelles ont été également considérées pour traduire les résistances au transfert de matière entre les phases gazeuse et solide. Certains modèles couramment utilisés, se sont avérés inadéquats, surtout pour les étapes à pression variable. Tout au long de ce travail, on a mis en exergue l'importance du choix de la cinétique de transport de matière pour avoir une simulation fiable. La confrontation des résultats expérimentaux et simulés pour l'adsorption de méthane et/ou de dioxyde de carbone en mélange avec l'hydrogène, montre une bonne concordance entre les deux. Les modèles conçus sont globalement satisfaisants et peuvent servir comme des outils pour la conception et le dimensionnement des procédés AMP

博士
國立中央大學
化學工程與材料工程研究所
98
As the industry fastly developed, it made shortage of fossile energy and serious air pollution. It is important to find out the renewable energy and reduce the emission of gas pollutant. Hydrogen energy is one kind of non-polluting and renewable fuel. As the people demend for more hydrogen energy and discoved new hydrogen production technology, it increased the utilization of hydrogen energy. The first part of study is to simulate hydrogen purification by applying composite palladium membrane reactor combined with pressure swing adsorption (PSA) hybrid process. This membrane reactor is adapted to produce hydrogen from methanol steam-reforming, where the permeated membrane hydrogen is mixed with sweep gas. The gas mixture from the membrane reactor is then fed into a dual-bed six-step pressure swing adsorption process, filled with zeolite 5A for hydrogen purification. The new-shape-structured materials, carbon monoliths, are characterized by straight parallel channels separated by thin wall, high void fraction and large geometric surface area, resulting in a low pressure drop under high flow rate and large contact area. These properties make carbon monoliths have the advantage on adsorption application. The second part of this study simulates the dynamic adsorption of butane on carbon-coated ceramic monoliths under isothermal condition. The parameters considered in the mathematical model include the mass transfer coefficient to the channel wall, effective diffusion within the pore structure and the axial dispersion model. The adsorption is expressed by the Dubinin-Radushkevich isotherm. The effect on increasing thickness of carbon-coated layer could raise the amount of adsorbate, although the thicker carbon layer would take longer time for stream diffusion to reach the saturated adsorption and breakthrough. Then the third part of this study develops mathematic model and simulates the adsorption separation of butane/air and CO2/N2 on carbon-coated ceramic monoliths for pressure swing adsorption processes under isothermal condition. In the three-step butane/air PSA process simulation study, increasing the thickness of carbon coated layer can increase the butane purity and recovery at the same valve value operation, but increasing the feed pressure will decrease the butane purity and recovery. For the other five-step pressure swing adsorption process for CO2/N2 on carbon-coated monoliths, when the mass transfer resistance between the gas and solid phase is small than that in the carbon coated layer, using an idle step is useful to improve the CO2 purity with an appropriate idle step time. The fourth part of study simulates the adsorption separation of CO2 from flue gas with 17% CO2 and 83% N2 on a carbon monolithic adsorber for a three-step rapid pressure swing adsorption process, which operates in the sequence of adsorption, rinse and desorption, under isothermal condition. The simulation results exhibit that the rinse step with a CO2 rich stream should be employed to enhance product purity. As to the effect of step time, increasing the rinse step time shows the greatest effect on increasing purity and decreasing recovery of CO2. Additinally, decreasing adsorber length and increasing rinse pressure are beneficial to improving the CO2 purity in production, but the CO2 recovery decreases at the same time.

博士
國立中央大學
化學工程研究所
83
A valve equation was used to calculate the flow rates at the both ends of a adsorber. By means of the incorporation of the valve equation into the simulation of pressure swing adsorption (PSA), the pressure change during the pressure-changing steps can be predicted more accurately and the simulation becomes more robust. For air-MSC system, when comparing the simulation results with the published experimental data, good agreements were obtained. The simulation results of the valve equation approach were also compared with that of the frozen solid approach and linear pressure change approach on two air . separation system. To verify the applicability of the developed program on the system of air separation with 5A zeolite, the simulation results of breakthrough curves, dual-bed PSA, and four-bed PSA were compared with the experimental data in literature and a good presentation was given. The effect of purge rate and production rate on purity and recovery was also discussed for a four-bed PSA process. The mathematical method used to do the simulation above was the method of lines with adaptive grid points. Moving finite element method (MFEM) was applied to the simulation of a PSA process. The cyclic steady- state results of a PSA process by MFEM were compared with the published experimental data and reasonable agreements were obtained. It is the first time that the reasonable cyclic steady-state results was acquired for the application of MFEM on PSA processes. Method of characteristics is another mathematical method can solve stiff problem. Under the operation restrictions of complete the utilization of the adsorber at the end of the production step and complete purge of the adsorber at the end of purge step, the analytical solution of the recovery for a simple PSA process producing pure oxygen was calculated. This analytical solution with nonlinear uncoupled adsorption isotherms for a binary separation system is acquired first time in this study.

碩士
國立中央大學
化學工程研究所
82
Hydrogen has a lot of utilization in the oil refining industry. Union Carbide has proposal a six-bed pressure swing adsorption process for purifying hydrogen from the reformer off-gas. This thesis has applied the method of lines combined with the estimation of the spatial derivatives by cubic spline/finite differense, and with integration with respect to time by program feed gas. The linear driving force model with/without the consideration of bed pressure drop are included in the Fortran code. We simulated the Union Carbide process in Taoyunang factory of China Petroleum Corporation with the assumption of packing with the 20-60 mesh PCB activated carbon of Calgon corporation ( in fact, two adsorbents, A-zeolite and activated carbon were packed in the column. ) And the linear driving force model is assumed for hydrogen PSA with/without the consideration of bed pressure drop. The simulation results are in good agreements with experimental data obtained elsewhere, and show the reliability of this PSA simulate program. Then, modification of the process was also studied by the simulation package. Reducing the purge amount would not improve the performance of the PSA process. However, prolonging the time of adsorption step could recover the hydrogen from the reformer coffgas with better recovery ( 86% ) while maintaining the hydrogen purity requirement ( >99% ).

碩士
國立中央大學
化學工程研究所
81
RPSA (Rapid Pressure Swing Adsorption) 因具有較傳統 PSA 構造更簡 單，產能更高的優點，故極具發展為一般居家生活用品之潛力，如醫療用 氧氣的供給和改善室內空氣品質等。本次研究係以 60-80 mesh 大小的 5A 沸石 (zeolite) 作為吸附劑，藉壓力變化來達到分離空氣製造富氧 氣體的目的。實驗系統依塔長共分為短、中、長三組，針對不同塔長的循 環操作時間、產氣量、進氣壓力等操作條件做最適化的探討。實驗結果發 現，不同塔長有其不同的最適進氣時間，且排氣時間和進氣時間的比值 (E/F ratio)以在 1.5 到 2 之間最佳。產氣量愈大則因較低濃度波亦可 能被推出塔外，而導致富氧濃度降低。提高進氣壓力有助於氣體的分離， 但需考慮加壓的成本。加長塔長有助於富氧濃度的提高，但有其限制。文 中並與 Pritchard and Simpson (1986) 和 Jones and Keller( 1980) 所提之論文作一比較結果，頗為符合，顯見本實驗有相當的準確性。

Pressure Swing Adsorption (PSA) is a method of separating a mixture of gases into its various components. Cyclic pressure and flow variations, in the presence of a selectively adsorbent material, are used to concentrate one species or group of species at one end of an adsorbent filled vessel, while the other species or group of species is concentrated at the other end. When PSA is used in separating gases, the necessity of gas pressurization and depressurization implies that the process can become very energy intensive. This is especially true in low capacity systems that require small compressors and/or vacuum pumps. There are many ways in which traditional PSA processes have been modified in order to reduce the amount of pressurization energy that is lost. One method is to use high pressure gas from one adsorbent bed to pressurize another adsorbent bed. This "equalization" recovers some of the energy used to initially compress the gas. However, as the gas is throttled from one bed to the other, irreversibilities are introduced into the process. In this thesis, the irreversibilities that are due to throttling are separated from those which are inherent in the PSA process and cannot be removed. The work required to produce a certain amount of gas by various simple PSA cycles is compared to the reversible work required to produce that amount of gas, based on the availability (or exergy) of the gas. The ratio of the reversible work to the actual work required for the PSA cycle is defined as the second law efficiency, and is compared for three cycles: the Four-Step cycle, the Ideal Four-Step cycle, and the Ideal Three-Step cycle. The irreversible expansion of gas through throttling valves is shown to account for the majority of the energy losses of the Four-Step cycle. Useful work (represented by the increase in availability of the product and exhaust) is found to be very small compared with the work required by the cycles. The true bed losses, inherent in the PSA process, are found to be similar in magnitude to the useful work, but much less than the energy lost by the throttling irreversibilities. The work required per mole of product to separate the gases decreases as the pressure ratio increases, and the second law efficiency increases with pressure ratio. For the cycle with no energy recovery, the second law efficiency varies widely with the selectivity ratio. A high selectivity ratio (implying a low separation factor) implies more work is required for the separation and the second law efficiency is lower. For the cycles with full recovery of the expansion energy, the work required and the second law efficiency are relatively independent of the selectivity ratio. The equilibrium based semi-analytical results are confirmed by the use of a numerical "Multiple-Cell" model. This model is also used to show that diffusion does not affect the second law efficiency of a cycle when energy recovery is present.